> how many fossils there might be at total on earth

The number is both incalculable and vague - is a shark tooth enough to count as a fossil? How about diatoms and other microfossils?

Diatomaceous earth alone contains around 10^6-10^7 frustules (the shell of a diatom) per gram. If you count them as fossils then the lower bound is 10^18 fossils per year just in diatomaceous earth production (the fossils are ancient but we produce nearly a million tons a year in diatomaceous earth).

If you have a fossil, and break it in half, then do you now have two fossils?